Flu Activity Still Elevated Across US

By the end of March, influenza activity had decreased slightly but was still elevated across the country, according to the US Centers for Disease and Prevention (CDC).

Since October 1, 2015, the CDC has catalogued 1341 influenza viruses: 550 influenza A (H1N1)pdm09, 336 influenza A (H3N2), and 455 influenza B viruses. Influenza A (H1N1)pdm09 was the most common virus type seen in week 12 that ended on March 26, 2016, according to the CDC’s Weekly US Influenza Surveillance Report.

However, the percentage of respiratory specimens that tested positive for influenza in clinical laboratories has decreased, the report stated.

The proportion of deaths from pneumonia and influenza was below the epidemic threshold for the National Center for Health Statistics (NCHS) Mortality Surveillance System but above the system-specific epidemic threshold in the 122 Cities Mortality Reporting System.

Around 7.3% of the deaths that occurred during week 10 that ended March 12, 2016, were related to pneumonia and influenza. In contrast, 7.7% of deaths reported in week 12 were caused by pneumonia and influenza.

Health centers reported 3 pediatric deaths linked to influenza in week 12, compared with just 1 during week 11 that ended on March 19, 2016.

Throughout the 2015-2016 influenza season thus far, there have been a total of 33 pediatric deaths linked to influenza. One was reported in Puerto Rico and another in Chicago. There was another separate death in Illinois, plus 1 each in Louisiana, Michigan, Mississippi, Nebraska, New York, Tennessee, Texas, and Washington. There were 6 in California, 6 in Florida, 3 in Arizona, 3 in Minnesota, 2 in Nevada, and 2 in Indiana.

The CDC report added that during week 12, 29 states reported widespread influenza activity. A total of 18 states reported regional influenza activity, 2 states plus Washington, DC, reported local influenza activity, and West Virginia reported sporadic influenza activity.

^{Map courtesy of the US Centers for Disease Control and Prevention}

The normal baseline for outpatient visits for influenza-like illnesses is 2.1%, but the rate was up to 2.9% in week 12. Symptoms include a fever (temperature of 100°F or higher), plus a cough and/or sore throat.

Puerto Rico, New Jersey, and New Mexico reported high influenza-like illness activity, while New York City and 7 states reported moderate activity. There were 15 states with low activity and 26 states with minimal ILI activity.